There was no Jewish prohibition against consulting the stars, but sages questioned if astrology applied to Jews.

Astrology is the belief that human destiny is determined or at least affected by the stars and planets in the ascendancy when a person is born.
The ancient Egyptian and Babylonian astronomers studied the movements of the heavenly bodies and as a result the astrologers claimed to be able to predict the fate of human beings born under this or that star.

The prophet Jeremiah inveighs against the people of Israel resorting to the astrologers: "Thus saith the Lord: Learn not the way of the nations, And be not dismayed at the signs of heaven; For the nations are dismayed of them (Jeremiah 10:2)."

In the book of Isaiah the prophet declares "Thou art wearied in the multitude of thy counsels; Let now the astrologers, the stargazers, the monthly prognosticators, stand up and save thee from the things that shall come upon thee (Isaiah 47:13)."

Yet neither in these two passages nor in any other biblical passage is there an explicit prohibition against consulting astrologers and there is certainly no denial that astrology actually works. Before the rise of modern science, astrology was itself believed to be an exact science. It was accepted as true by the talmudic rabbis, for example, who debated only whether the Jewish people are immune, in miraculous fashion, to the influence of the stars: "There is no mazal (planet and its influence) for Israel."

Even the medieval Jewish philosophers were not inhibited by their rationalistic approach from believing in the power of the stars. Maimonides was an exception, but he rejected astrology on theological grounds, that such belief was contrary to the doctrines of divine providence and human freewill. When Maimonides was asked in a letter how he could deny the truth of astrology since the talmudic rabbis held to this belief, he replied that man was created with eyes in the front of his head, not the back!

Maimonides does refer to the zodiac but only in the astronomical, not the astrological, sense. In addition, Maimonides holds that the biblical objections to magic and divination extend to astrology. He is followed in this by the Shulhan Arukh (Yoreh Deah, 179.1) where the ruling is given: "One must not inquire of the astrologers and not consult lots."

But Moses Isserles, in his gloss to this (179.2), quotes Nahmanides to the effect that one must not consult the astrologers but rely on God without being concerned about what the future will bring. Nevertheless, if a man knows some undertaking to be contrary to his mazal, his fate as determined by the stars, he should take the necessary precautions and should not rely on a miracle to save him. It follows that there has been in the past a somewhat ambivalent attitude towards astrology, only Maimonides declaring it to be complete nonsense.